The present invention relates to methods and apparatus for changing the repetition rate of image data, as well as to methods and apparatus for detecting still images and scene changes in image data.
A known image data reproduction device reproduces image data at a variable speed as a sequence of fields whose repetition rate varies with respect to the repetition rate of the fields as output by the device for display. The reproduction device serves to absorb the differences in the repetition rates between the reproduced image data and the output image data by omitting or adding fields by means of a frame synchronizer, such as that which is disclosed in Japanese Laid Open Patent No. 136384/1986.
However, in this device the omission or addition of the fields occurs randomly, so that image discontinuity can become apparent to the viewer. This effect is illustrated with reference to FIG. 1. In FIG. 1, the fields of the image data as reproduced are represented schematically by the sequence (A) as a succession of fields F1 through F8 having the respective image data content "A" through "H". If it is assumed that one of these fields (in this example, field F4 having the image data content D) is omitted in order to reduce the field repetition rate, as illustrated by the sequence (B) in FIG. 1, it will be seen that a discontinuity is produced between the fields F3 and F5 in sequence (B). Where the fields depict rapid image movement, the discontinuity caused by omitting the field F4 becomes apparent, so that a sense of awkwardness in the image produced by the sequence (B) is unavoidably produced.